A model system for the study of human retinal angiogenesis: activation of monocytes and endothelial cells and the association with the expression of the monocarboxylate transporter type 1 (MCT-1).

Aims/hypothesis: The growth of retinal vessels is associated with a number of disease conditions, including diabetic retinopathy and proliferative vitreo-retinopathy. In this study we describe a model of human retinal angiogenesis and show how this may be used to explain the mechanisms that are associated with the growth of new retinal vessels.
Methods: A 4 mm diameter disc of retinal tissue was placed within a fibrin matrix and the appearance was monitored daily by light microscopy. Immunohistochemical techniques were used for the detection of, glial fibrillary acidic protein, CD68, the Ki-67 antigen, vascular endothelial growth factor, monocarboxylate transporter type 1 and von Willebrand's factor.
Results: Vessels were evident extending from the periphery of the explant and the activation of endothelial cells was shown by immuno-peroxidase staining of paraffin embedded sections of the explants for the expression of the Ki-67 antigen, a marker of cell proliferation. The expression of glial fibrillary acidic protein and von Willebrand's factor increased with duration in culture and the presence of activated macrophages or microglia or both was shown by positive immunoreactivity for CD68 and Ki-67 and were identified by day 3. The presence of endogenous vascular endothelial growth factor and the activation of monocarboxylate transporter type 1 by vascular endothelial growth factor, showed the involvement of specific growth factors.
Conclusion/interpretation: The explant model provides evidence for the involvement of macrophages and glial fibrillary acidic protein activation in human retinal angiogenesis and for the expression of monocarboxylate transporter type 1, which is likely to be important in the use of lactate in the hypoxic retina.